1. Field of the Invention
The present invention relates to a file reading method and a file requesting client device to be used in a client-server information communication system formed by a file server which realizes a file providing service and a file requesting client which issues a file transfer request to the file server and cache the file transferred from the file server in response to that file transfer request into its own cache region.
2. Description of the Background Art
The WWW (World Wide Web) is a known file providing program which provides files such as documents from a server to a client through the Internet. The WWW comprises a WWW server and a WWW client, and provides files such as documents from the WWW server to the WWW client according to the prescribed file transfer protocol called HTTP (HyperText Transfer Protocol).
In general, a file transfer through a network is associated with problems such as a considerable amount of transfer time required and an increase of traffic in the network, so that it is preferable to avoid unnecessary file transfer as much as possible.
For this reason, there is a type of WWW client which has a function for transmitting a file transfer request according to HTTP to the WWW server, and temporarily storing a file transferred from the WWW server in response to that file transfer request into a local file storage region within its own storage medium called cache. Then, when another file transfer request for the same file occurs, the WWW client notifies the creation date and time of the cached file to the WWW server. At the WWW server, the notified creation date and time are compared with the creation date and time of the requested file, and if the creation date and time coincide, this fact is notified from the WWW server to the WWW client. In response, the WWW client reads out the corresponding file from its own storage medium. In this manner, the file is transferred from the WWW server to the WWW client only when the creation date and time do not coincide, i.e., the requested file has been updated since it was originally transferred from the WWW server to the WWW client, so that it is possible to reduce traffic in the network.
However, under the circumstance in which the WWW client cannot make a normal access to the WWW server as in a case where the client side computer is not connected to the network, the files stored in the cache cannot be utilized even when the stored files include a file requested by the file transfer request according to HTTP.
This is because the conventional WWW client has such a configuration that, when the file transfer request in the HTTP format is received, even if the requested file is stored in the cache of this conventional WWW client, it is necessary for this conventional WWW client to communicate with the WWW server in order to ascertain whether the cached file is the latest one or not, and when an access for this purpose is not carried out normally, a communication error message is presented to a user. Consequently, in the conventional WWW client, the cached file cannot be utilized unless the access to the WWW server is carried out normally.
On the other hand, the present inventors recently proposed a new file transfer method in which a file requested by a user as well as its related files are transferred from the server to the client together in response to a single file transfer request (see Japanese Patent Application No. 7-292910 (1995) for detail). According to this new file transfer method, a transfer of multiple files from the server to the client can be realized by a single command from a user, without requiring a user to specify files to be transferred one by one. Using this new file transfer method, it is possible to realize an efficient file caching scheme in which those files (related files) which are likely to be requested by a user later on are cached in advance in the client computer. This scheme is particularly effective in a case where the client computer is a device such as a portable terminal which is not necessarily used under an environment in which a connection to a network is always possible.
With this new file transfer method, however, the similar problem as described above also arises at a time of utilizing the cached files. Namely, any of the cached files cannot be utilized unless the access to the WWW server is carried out normally.
It is to be noted here that, in a case of Netscape Navigator (registered trademark), a user has an option to require the checking as to whether the cached file is the latest one or not. When this checking is required, if no response is received from the server for some reasons such as the server is not in operation or the connection to the network is disconnected, no cached file will be displayed at the client. When this checking is not required, the cached file will be displayed without requiring a network access.